A hung moving blanket is a useful midrange absorber and a poor low-frequency one, so it fixes a bright, reflective room and does nothing about rumble, traffic or an air handler.
Sound blankets: what a moving blanket does to a room
checked 2026-09-16responsible Room Tone Register (a named register, not a person)
The octave-band table
| Octave | α, single layer | α, two layers | α, hung 100 mm clear of wall |
|---|---|---|---|
| 125 Hz | 0.10 | 0.15 | 0.25 |
| 250 Hz | 0.25 | 0.35 | 0.40 |
| 500 Hz | 0.35 | 0.50 | 0.55 |
| 1 kHz | 0.50 | 0.65 | 0.65 |
| 2 kHz | 0.55 | 0.70 | 0.70 |
| 4 kHz | 0.60 | 0.75 | 0.75 |
Two facts fall out of the table. First, doubling the material is worth less than the first layer almost everywhere. Second, hanging the same single layer with an air gap behind it beats a second layer in the bottom two octaves, because the gap lets the material sit where the air is actually moving.
The two ways they are used on set
- As a wall covering behind and beside the microphone, to reduce the reflections that arrive soon after the direct sound. This works, in the midrange, and it is the common use.
- As a barrier between the microphone and a source in the next room or in the corridor. This mostly does not work: a blanket is light, and mass is what stops airborne sound. It reduces high-frequency leakage and passes almost everything else.
What they cannot do
They cannot lower the noise floor of a room whose problem is a compressor, a fan or traffic. Those sources put their energy below 250 Hz, where the blanket's coefficient is 0.10 to 0.25. If the floor is 44 dB(A) because of an air handler, hanging blankets will not move the meter, and the session will still fail. The only fixes for that are switching the source off or moving.
A blanket also reflects almost nothing at high frequency, so a room fully lined with them can become dull rather than dry. The useful target is reducing the early reflections without deadening the top octave entirely — which usually means covering part of the room, not all of it.
Near kin: panels, traps and gobos
A rigid porous panel behaves like a blanket but keeps its thickness, which is what sets its low-frequency limit. A bass trap is a different mechanism aimed at the octaves a blanket cannot reach. A gobo is a portable screen, and its job is usually to block line of sight for the microphone rather than to absorb the room. Mass-loaded vinyl adds mass and therefore blocks transmission; it is not an absorber.
| Term | What it is | How it differs from a blanket |
|---|---|---|
| Rigid panel | A porous absorber with fixed thickness | Keeps its depth, so it reaches lower |
| Bass trap | A device aimed at the low octaves | A different mechanism, not more of the same |
| Gobo | A portable screen | Usually blocks line of sight, absorbs less |
| Mass-loaded vinyl | A dense barrier | Blocks transmission; does not absorb |
The common misread is expecting a blanket to lower a noise floor that comes from an air handler, traffic or a compressor. Those sources put their energy below 250 Hz, where a blanket's coefficient is 0.10 to 0.25. The meter will not move, and the session will still fail. Blankets fix reflections; they do not fix sources.
Source log
- 01Early Reflections, Physical Audio Signal Processing (CCRMA, Stanford)supports the role of early reflections in the perceived sound of a room
- 02Themes in the Sonic Studio Handbook (SFU)supports the vocabulary used to describe the effect of absorption on a space
- 03Standing Waves, Penn State Acousticssupports the standing-wave behaviour that makes an air gap matter
Each line points at one specific document. No line is a home page.
Leave this page Close this page if the room's problem is low-frequency noise rather than reflections — blankets will not move that meter.